字幕表 動画を再生する 英語字幕をプリント For a long time the measurement of a healthy baby was having 10 fingers and 10 toes. Wait, why didn't anybody care about the eyes, nose, or anything else? Hey digitals, Lissette here for Dnews. I am the proud owner of 10 fingers and 10 toes, I can prove half of this just right now. You’ll just have to trust me on the 10 toes thing. But, have you ever wondered why that is? Why don’t we have 12 fingers and 14 toes? Or 6 fingers and 1 toe? Well, this may not come as a shocker to you DNews fans out there, but no one really knows. It might all come down to math. Mark Changizi, a theoretical neurobiologist, developed a hypothesis called the Limb Law, first published in the Journal of Theoretical Biology in 2001. It’s a mathematical equation that tries to figure out the correct number of limbs an animal needs in order to connect to the world around it based on the length of its limbs relative to it’s body size. Okay, wow. The equation looks like this. Confusing, I know. But he used this equation with 190 different animal species from seven different animal Phyla, and the math seems to check out. Mark thinks this same equation could be used to figure out why humans have five fingers on each hand. The calculation treats our palms as the animal and our fingers as limbs. Also it takes into account that the whole reason behind having fingers is that they’re able to fold over our entire palm, in order to grasp things. So, first, fingers have to be at least as long as our palms, also known as length need to connect to the outside world. When you crunch the numbers, you'll get 9.42 digits per hand. But, he argues, since our hand is not a free roaming creature, but is attached to our arm, it doesn't need limbs protruding from all sides. Hands only need half the total number of limbs. That gets us to 4.71 fingers per hand. Just based on math. Pretty amazing. But other explanations are simpler than that. Evolutionary biologists say that we have 10 fingers and 10 toes because that’s the best combination for us. If 8 fingers and 8 toes would have given us an evolutionary advantage, humans would have 4 fingers on each hand. Cliff Tabin, a Harvard Medical school geneticist focusing on limb development in vertebrates, pointed out that our motor skills come down to our thumb and index finger, and that another small, 6th finger wouldn’t really change anything. And if we ever did grow a 6th finger, Tabin argues, it would probably grow out of our wrists, like panda’s . It gives them extra support when gripping bamboo, which gives them an evolutionarily advantage. So, basically, we'd have six if people with six fingers got an advantage. Then, there is this more complicated science answer to why we have the number of digits we do. James Sharpe from the Centre for Genomic Regulation in Barcelona discovered it all comes down to three molecules in our body. Bmp, Wnt and Sox9. They’re responsible for marking out in an embryo where fingers will go and how far apart they’ll grow. And for the most part it marks out space for five fingers on each hand and five toes on each foot. But of course sometimes things can go wrong, resulting in the gaps between fingers being bigger and only having room for four fingers. Or, sometimes it screws up and you have room for an extra finger. Oh and fun fact, the basis for this discovery was a theory first proposed by Alan Turing back in 1952 about how animals get their spots and stripes. Love you, Alan. So why 10 fingers and 10 toes? Again, we’re still not entirely sure. But it all seems to come down to because that’s exactly the number of fingers and toes we need. Sometimes it’s best to just trust evolution and be thankful we don’t have hoofs. Amirite? So that’s hands. But what about feet? When did they evolve and why do they look different from hands? Julia walked a mile in those shoes, here. Toes likely evolved from the same bones that became fins, wings and hoofs in other species. The dominating scientific theories are that fingers and toes are exclusive features of tetrapods. Or vertebrates with limbs. But according to one study toes may evolve even before our fishy ancestors left the ocean. Why do you think we have 10 fingers and toes? Would you rather have more or less? Let us know on the comments and remember to subscribe to DNews for more episodes everyday. Thanks for watching, guys.